In a wireless network comprising a plurality of network nodes, it is desirable to achieve high capacity and adequate performance in communication with wireless devices. For example, the operation of the network nodes can be made more efficient by establishing neighbour relations between network nodes so they can communicate directly with each other instead of using an intermediate core network or the like, e.g. to support and facilitate handover of wireless devices from one network node to another.
The term “wireless network” is used in this description to denote any network comprising network nodes such as base stations, access points, eNodeBs or the like which are capable of radio communication with wireless devices, e.g. by transmitting data and control information as well as reference signals that can be detected and measured by the wireless devices for evaluation of connections and channels. The nodes in the network that perform such radio communication with wireless devices are also generally denoted “network nodes” herein. Further, the term “wireless device” denotes any communication equipment that is capable of radio communication with network nodes in a wireless network. Some non-limiting examples of wireless devices that may be involved in the procedures described herein include mobile phones, smartphones, tablets, laptop computers and Machine-to-Machine, M2M, devices such as sensors and actuators. Throughout this description, the term “User Equipment”, UE, may also be used instead of wireless device.
In order to evaluate whether a connection to a network node is suitable for communication and to configure various parameters for the communication, the wireless devices are required to perform measurements on predefined reference signals which are regularly transmitted from the network nodes, and to send measurement reports to a serving network node. These measurement reports are then used by the network nodes as a basis for making various decisions and settings, including handover and/or beam-switching decisions. In this description the reference signals are sometimes referred to as “Mobility Reference Signals”, MRSes, which term is commonly used in this field.
Despite advanced radio network planning tools, it is very difficult to predict the radio propagation in detail and to identify network nodes between which handovers may potentially occur. As a consequence, it is difficult to determine which network nodes that need to have a relation and maybe also a direct connection for communication, e.g. prior to deployment of the network. In this description, the term “neighbour relation” is used to indicate that two neighbouring network nodes have a direct connection to one other, such as an X2 connection or interface as defined in Long Term Evolution, LTE, that can be used for communicating messages rapidly and directly with each other. A neighbour relation further indicates that the two neighbouring network nodes have certain knowledge about each other's configurations and characteristics. For example, each network node need to know a mapping of the neighbouring network node's reference signals to its IP address. Further, two neighbouring network nodes should be able to exchange various information over the connection to support mobility, interference management, etc.
The above issues have been addressed in LTE, where wireless devices could be requested to retrieve information such as a unique node identifier, also referred to as a “global” identifier, from system information broadcasted from unknown network nodes that have been recently installed, and to report the retrieved system information to the serving network node. Such information could then be used to convey messages from the serving network node to the unknown network node via the core network which maintains a lookup table from a unique node identifier to an established S1 connection. One such message was used to request transport network layer address information necessary for a direct network node to network node connection for the X2 interface. To achieve smooth operations of the mobility procedure in the network, each network node needs to have a concrete and up-to-date list of its neighboring network nodes which can be handover candidates for the wireless devices, as provided by the neighbour relations.
In LTE, establishment of neighbour relations is based on “always-on” reference signals, i.e. the reference signals are constantly transmitted so that they can be detected and read at any time. However, in a wireless network where the reference signals are not always-on by design, e.g. in order to minimize the amount of system control signaling in the network, the existing LTE solutions cannot be used. As a result, the unique global identifier, which should normally be transmitted over the network according to previous LTE technology, may not be available and used for a newly established network node. The global identifier was necessary to establish a neighbor relation according to conventional LTE technology. It is further a problem that a neighbor relation cannot be established in an efficient and simple manner without substantial impact on the operation of the network and/or the wireless devices.